U.S. Senate Judiciary Committee Chairman Patrick Leahy on Tuesday proposed a gay rights amendment to the Senate's immigration bill, prompting one of the measure's Republican sponsors to repeat his prediction that it could sink the legislation.

"It'll kill the bill," Florida Senator Marco Rubio said in a brief interview. "There is a coalition of groups who are supporting immigration reform who will not support it if that's in there."

Rubio, the son of Cuban immigrants and a possible Republican presidential candidate in 2016, is key to attracting conservative support for the bill. It remained uncertain whether the amendment would make it through the committee, which is controlled by Democrats.

The Leahy amendment, one of more than 100 offered two days before the Judiciary Committee takes up the bill, would allow U.S. citizens who are in "long-term committed relationships" to sponsor their foreign partners for green cards, which would allow them to live and work legally in the United States.

Leahy could ultimately decide to delay the fight over the gay rights amendment until the immigration legislation comes before the full Senate, instead of offering it in his committee.

The comprehensive immigration bill is the work of four Democrats and four Republicans in the U.S. Senate, including Rubio.

It would provide a path to legal status and ultimately citizenship for some 11 million undocumented foreigners now in the United States and tighten border security to stem the flow of illegal immigrants in the future.

The bill's provisions to increase the flow of both skilled and unskilled workers from abroad have attracted heavy support from industry, particularly from technology companies and agri-business, which say they face workforce shortages that are making the United States less competitive.

The bill's parts are interdependent politically, so that the defeat of one could result a loss of support for the others during a difficult obstacle course that begins with the Judiciary Committee. A flood of amendments poured into the committee Tuesday.

SCORES OF AMENDMENTS

Senator Orrin Hatch of Utah, a senior Republican on the panel, submitted 24 amendments, including one to clamp down on the cultivation of marijuana on federal lands and another to require DNA identification for every adult illegal immigrant who could earn legal status under the legislation.

Hatch also wants to double fees, to $1,000, for a "green card" providing permanent residency, the final step toward citizenship.

The second-ranking Republican in the Senate, John Cornyn of Texas, offered nine amendments, most of them aimed at bolstering border security, a party aide said.

Cornyn would require that federal agencies jointly certify "full situational awareness" and "operational control" of the southern border with Mexico for at least a year before granting legal status to any of the 11 million undocumented immigrants. Democrats are likely to oppose that measure as being unachievable.

The existing bill would allow the pathway to citizenship to begin promptly after being enacted into law, instead of Cornyn's minimum one-year wait.

Cornyn also proposed ways to ensure a smoother flow of commerce at the U.S.-Mexico border by reducing wait times for trucks ferrying goods.

Currently, some U.S. trucks packed with goods are in line for several hours, slashing profit margins.

"Senator Cornyn is offering 'no poison bills,'" an aide said. "What he wants to do is improve border security."

Republican Senator Jeff Sessions, an outspoken opponent of the bill, offered dozens of amendments, including one to reduce the number of foreign low-skilled workers entering the United States under the bill.

This was a delicately negotiated provision signed off on by the AFL-CIO labor organization and the U.S. Chamber of Commerce.

Meanwhile, Senator Charles Grassley of Iowa, the senior Republican on the panel, offered 77 amendments, among them provisions to strengthen the bill's border security and ensure employment verification.

Democrats control the committee, 10-8, and two of the Republicans, Jeff Flake and Lindsey Graham, are co-sponsors of the bill.

A senior Republican aide said the committee makeup would likely block any amendment intended to kill the bill a so-called poison pill.

Those amendments would likely be rejected by votes of 12-6, with Flake and Graham joining the 10 Democrats in opposing them, the aide said.

But such amendments may be attempted when the bill reaches the full Senate in June. Democrats control the chamber, however, and could try to prevent or at least limit how many are voted on.